Alarm system for the safety of non-swimmers

ABSTRACT

An alarm system for the safety of non-swimmers comprises a portable transmitter which is adapted to be attached to the body of the non-swimmer and to be activated on immersion in water, and a receiver adapted to operate an alarm on receiving the transmitted signal. The transmitted signal is a mechanical wave having a frequency which is ultrasonic.

United States Patent 1 1 3,810,146

Lieb May 7, 1974 ALARM SYSTEM FOR THE SAFETY OF NON-SWHMMERS [56]References Cited [75] Inventor: Solomon Nathan Lieb, UNI D STATESPATENTS Johannesburg, South Africa 3,273,138 9/1966 Kolm 340/261 [73]Assignee: Manfred Dworcan, Johannesburg, I

South Africa; a part interest Primary Exammer-John W. Caldwell AssistantExaminerGlen R. Swann, III Filedi 13, 1972 Attorney, Agent, or FirmEricH. Waters [21] App]. No.: 314,839

[57] ABSTRACT An alarm system for the safety of non-swimmers com- 30 F Al t P t D t 1 Drag pp "on y a a prises a portable transmitter which isadapted to be Mar. 22, 1972 South A rlca 72/1956 attached to the y ofthe nomswimmer and to be activated on immersion in water, and a receiver[52] Cl 340/ 24 243 adapted to operate an alarm on receiving thetransmit- 51 I t Cl Gosh 21/00 2 ted signal. The transmitted signal is amechanical wave l C having a frequency which is ultrasonic. [58] Fieldof Search 340/261, 279, 235, 283,

340/416, 42]; 9/313 13 Claims, 5 Drawing Figures WM MAM saw/3W FIELD OFTHE INVENTION FIG. is the alarm circuit.

DETAILED DESCRIPTION FIG. 1 shows the alarm system comprising atransmit- This invention relates to an alarm system for the 5 ter 10, asensor 12, a tuned amplifier 14, an alarm cirsafety of non swimmersexposed to open water.

BACKGROUND An open body of water such as a swimming pool represents adanger to small children who cannot swim, and is a source of constantanxiety to parents of such children.

Unprotected swimming pools have been the cause of many small childrenloosing their lives, and with the rapid increase in the number ofprivately owned pools it has become necessary for some local authoritiesto legislate for the compulsory provision of protective fencing aroundsuch pools.

SUMMARY OF THE INVENTION It is an object of this invention to provide analarm system to indicate entry of a child entering into a body of water.

It is a further object of the invention to provide a method of detectingthe entry of a non-swimmer into the water of a swimming pool.

An alarm system for the safety of non swimmers according to theinvention comprises a portable transmitter adapted to be attached to thebody of a nonswimmer, means on the transmitter to actuate thetransmitter on immersion in a body of water, a sensor adapted to beimmersed in the body of water and further adapted to sense the output ofthe transmitter when actuated and, means to amplify the sensed signaland operate an alarm located out of the body of water.

Preferably the actuating means on the transmitter comprises two exposedelectrodes on the transmitter adapted to be electrically bridged by theelectrical conductivity of the water. The output stage of thetransmitter may suitably consist of an electromechanical trans ducercapable of producing ultrasonic mechanical waves. Similarly the sensormay be a transducer capable of converting the sensed signal from thetransmitter into an electrical signal which is then fed to theamplifying means to drive the alarm. The transmitted signal ispreferably of a specific frequency and the amplifying means is adaptedto respond only to signals of that frequency. Further according to theinvention the system is included in a swimming pool.

Further according to the invention there is provided a method ofdetecting the entry ofa non-swimmer into a swimming pool which consistsin the steps of generating an underwater signal in the pool on immersionof the non-swimmer in the pool water, detecting the signal at a fixedunderwater point in the pool, and adapting the signal to operate analarm outside the pool.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be describedwith reference to the drawings in which:

FIG. I is a diagramatic view illustrating the components of the system,

FIG. 2 is a perspective view of the transmitter housing,

FIG. 3 is a circuit diagram of the transmitter,

FIG. 4 is the amplifier circuit, and

cuit 16 and a loudspeaker 18.

The transmitter circuit which is seen in FIG. 3 includes a replaceablemercury battery 20, two spaced electrodes 22 and 24, a switchingtransistor 26, a modified tuned collector oscillator consisting oftransistor 28 and a tuned circuit 30, and a barium-titanateelectro-mechanical transducer 32.

The transmitter circuit is encapsulated in a small waterproof buttonshaped housing 34, see FIG. 2, made from epoxy resin. The electrode 22is in the form of an exposed metal disc attached to one face of thehousing and the electrode 24 is similarly exposed on the opposite sideof the housing. The electrode 24 is in contact with the positiveterminal of the battery 20 and forms the cover of the compartment inwhich the battery is housed.

The housing 34 of the transmitter includes a loop 35 to which a suitablechain orthe like is attached to enable the transmitter to be securelyattached to the clothing or body of a non-swimmer.

When the transmitter is not immersed in water, the base of thetransistor 26 is floating and the transistor is biased to cut-off, thereis consequently no base bias on the transistor 28 and the transmitter 10is inoperative. If the transmitter is immersed in water, the electricalconductivity of the water bridges the exposed electrodes 22 and 24 and apath is formed from the positive terminal of the battery to the base oftransistor 26 thereby switching it to supply a base bias to transistor28. The oscillator circuit 30 is slug tuned to oscillate at 65 Kc/s andto produce a signal of approximately 20 volts peak to peak across thetransducer 32. The transducer which is encased in the epoxy resin of thehousing 34 will vibrate at the oscillator frequency. The vibration willbe transmitted through the housing and create mechanical waves in thewater having a frequency corresponding to that of the oscillator.

The sensor 12 (FIG. 4) is a barium-titanate electromechanicaltransducer. This transducer is also encapsulated in epoxy resin forwaterproofing. The sensor 12 is connected by means of a co-axial cable36 to the tuned amplifier 14.

The tuned amplifier 14 includes three transistors 38, 40 and 42 whichmake up a conventional three stage amplifier, transistors 44 and 46which are collector tuned to 65 Kc/s, a further amplifier transistor 50,two transistors 52 and 54 connected as a Darlington pair and a relay 56.

The amplifier stage comprising transistors 38, 40 and 42 is adapted tobe over-driven to provide a limited signal at the collector oftransistor 42 when only background noise is picked up by the sensor 12.When an input signal having a frequency of 65 Kc/s is picked up by thesensor 12, the signal at the collector of transistor 42 is accepted bythe tuned circuits of transistors 44 and 46 and a signal is developedacross a sensitivity control 48. This signal is further amplified bytransistor 50 and fed to the transistors 52 and 54 to operate the relay56 which energizes the alarm operating circuit 16.

The alarm operating circuit 16 (FIG. 5), though shown seperately in FIG.1, is built into the same case as the amplifier circuit 14, and consistsbasically of a uni-junction transistor 58 which modulates an astablemulti-vibrator oscillator consisting of transistors 60 and 62 directlycoupled to an output stage consisting of transistors 64, 66 and 68 whichdrive the loudspeaker 18. As mentioned above. when the relay 56 of theamplifier circuit closes, the alarm circuit is energized. The oscillatorcircuit of the transistor 58 will now function and is adapted tooscillate at about four cycles per second and produce a saw-tooth waveform. Base currents for transistors 60 and 62 are likewise varied andconsequently the frequency of oscillation of the multivibrator is alsovaried. This varied signal is then fed to the output stage of thecircuit to drive the loudspeaker 18. The alarm produced by this circuitis distinctive and is unlikely to be confused with other alarms.

In use, referring again to FlG. l, the sensor 12 is partially embeddedin the wall of a swimming pool 72 below the waterlevel. The co-axialcable 36 connects the sensor to a unit 74 which houses both theamplifier and alarm circuits 14 and 16 and is in turn connected to theloudspeaker 18. The unit 74 and the loudspeaker are situated away fromthe pool 72. The transmitter is attached to the body of a non-swimmer76.

The unit 74 is continuously in the on condition and when the person 76enters the water of the pool 72 the transmitter 10 will be actuated asdescribed above and transmit mechanical waves having a frequency of 65Kc/s throughout the area of the pool within the confines of the water.This signal will be picked up by the sensor 12 and operate the alarm asdescribed above.

To ensure positive functioning of the system a test circuit could beincluded in the circuitry of the transmitter l0 and the unit 74.

The invention is not limited to the precise constructional details asherein described. The unit 74 could for example be water-proof andlocated in the water or wall of the pool, alternately the sensor 12 neednot be embedded in the wall of the pool and could. for example, besuspended in the water from the side of the pool by the co-axial cable36.

I claim:

1. An alarm system for the safety of non-swimmers comprising a portabletransmitter adapted to be attached to the body of a non-swimmer. meanson the transmitter to actuate the transmitter on immersion in a body ofwater, a sensor adapted to be immersed in the body of water and furtheradapted to sense the output of the transmitter when actuated, and meansto amplify the sensed signal and operate an alarm located out of thebody of water.

2. An alarm system as claimed in claim 1 in which the actuating means onthe transmitter comprises two electrodes which are adapted to beelectrically bridged by the electrical conductivity of the water.

3. An alarm system as claimed in claim 2 in which the electrodes areexposed to the water.

4. An alarm system as claimed in claim 2 in which the transmitter has anoutput stage in the form of an electro-mechanical transducer.

5. An alarm system as claimed in claim 4 in which the output frequencyof the transducer is ultrasonic.

6. An alarm system as claimed in claim 5 in which the frequency is inthe range 50 7O Kc/s.

7. An alarm system as claimed in claim 1 in which the sensor comprisesan electro-mechanical transducer.

8. An alarm system as claimed in claim 6 in which the amplifying meansis frequency-selective.

9. An alarm system as claimed in claim 1 in which the alarm comprises aloudspeaker.

10. A swimming pool alarm system for the safety of non-swimmerscomprising a portable transmitter adapted to be attached to the body ofthe nonswimmer, means on the transmitter to actuate the transmitter onimmersion in the swimming pool water, a sensor situated below thesurface of the swimming pool water and adapted to sense the output ofthe transmitter when actuated, means connected to the sensor and adaptedto amplify the sensed signal and an alarm situated out of the swimmingpool water connected to the amplifying means and adapted to be operatedby the amplifying means in response to the sensed signal.

11. A swimming pool alarm system as claimed in claim 10 in which thetransmitter actuating means comprises two electrodes on the transmitterwhich are adapted to be electrically connected by the conductivity ofthe swimming pool water.

12. A swimming pool alarm system as claimed in claim 10 in which thetransmitter output stage comprises an electromechanical transduceradapted to vibrate at a predetermined ultrasonic frequency.

13. A swimming pool alarm system as claimed in claim 10 in which theamplifier is tuned to receive only the frequency of the signaltransmitted by the transmitter.

1. An alarm system for the safety of non-swimmers comprising a portable transmitter adapted to be attached to the body of a nonswimmer, means on the transmitter to actuate the transmitter on immersion in a body of water, a sensor adapted to be immersed in the body of water and further adapted to sense the output of the transmitter when actuated, and means to amplify the sensed signal and operate an alarm located out of the body of water.
 2. An alarm system as claimed in claim 1 in which the actuating means on the transmitter comprises two electrodes which are adapted to be electrically bridged by the electrical conductivity of the water.
 3. An alarm system as claimed in claim 2 in which the electrodes are exposed to the water.
 4. An alarm system as claimed in claim 2 in which the transmitter has an output stage in the form of an electro-mechanical transducer.
 5. An alarm system as claimed in claim 4 in which the output frequency of the transducer is ultrasonic.
 6. An alarm system as claimed in claim 5 in which the frequency is in the range 50 - 70 Kc/s.
 7. An alarm system as claimed in claim 1 in which the sensor comprises an electro-mechanical transducer.
 8. An alarm system as claimed in claim 6 in which the amplifying means is frequency-selective.
 9. An alarm system as claimed in claim 1 in which the alarm comprises a loudspeaker.
 10. A swimming pool alarm system for the safety of non-swimmers comprising a portable transmitter adapted to be attached to the body of the non-swimmer, means on the transmitter to actuate the transmitter on immersion in the swimming pool water, a sensor situated below the surface of the swimming pool water and adapted to sense the output of the transmitter when actuated, means connected to the sensor and adapted to amplify the sensed signal and an alarm situated out of the swimming pool water connected to the amplifying means and adapted to be operated by the amplifying means in response to the sensed signal.
 11. A swimming pool alarm system as claimed in claim 10 in which the transmitter actuating means comprises two electrodes on the transmitter which are adapted to be electrically connected by the conductivity of the swimming pool water.
 12. A swimming pool alarm system as claimed in claim 10 in which the transmitter output stage comprises an electromechanical transducer adapted to vibrate at a predetermined ultrasonic frequency.
 13. A swimming pool alarm system as claimed in claim 10 in which the amplifier is tuned to receive only the frequency of the signal transmitted by the transmitter. 